Various communication schemes are available which allow a plurality of individual asynchronous systems to communicate with each other. Some such schemes allow for multiple access to a communication line or channel so that a certain number of remote systems may access a base system at one time, or may access each other through a base system at any given time without interfering with each other. In such multiple access systems, generally a communication channel or line is shared by the various remote systems. In order to avoid interference on the channel when several systems are using it, the channel is usually divided such that each specific remote system in the overall communication network will only be using the channel under specific parameters which are different from the parameters associated with another system on the channel. That is, only one remote system will be on the channel at any given time.
Various different ways of dividing a channel have been derived and are known in the art. For example, the channel might be divided by frequencies such that each of the respective remote systems in the communication scheme is allocated a different frequency. Such a system is often referred to as a frequency division multiple access (FDMA) communication scheme. Alternatively, in a time division multiple access (TDMA) communication scheme, a number of systems can communicate on the same frequency channel or a plurality of channels, but at different times.
That is, each system has some time divided portion of the channel. Each system knows the particular time during which it may transmit and receive information, and each system therefore acts accordingly to operate within a particular time slot. The use of a TDMA scheme makes very efficient use of the communication channels because multiple systems may use the same frequency channel at the same time without interfering with one another.
More specifically, within a TDMA system, the access time on the channel is divided into a plurality of continuously repeated TDMA frames. Each frame is divided into a variety of slots, with certain slots being allocated for a particular remote system to utilize in transmitting and receiving data. Generally, within each frame, a system which is communicating will have a slot designated in which it will transmit information and another slot designated in which it will receive information. The signals transmitted and received by the respective systems take the form of intermittent signals called “bursts.” The bursts, often referred to as packets, are repeated in regular periods corresponding to those respective slots of the TDMA time frame and it is required that such burst signals be properly synchronized in the slots of the frame so as not to overlap each other and cause interference between the systems. Therefore, each station transmits or receives its bursts of communication only within the time slots of the frame that are allotted thereto, so the communication between the respective systems can be performed on the time division basis without any time overlap of the signals transmitted from the various communication systems.
In order to maintain such a time-division communication, it is essential for each system to reliably control its bursts of communication to be correctly transmitted and received within particular time slots of a frame. TDMA communications are usually controlled according to the timing of a master system. That is, the master system defines the length of the frame and the boundaries of the frame and the particular time slots therein which may be utilized by remote systems or slave systems to send or receive their packets. Specifically, when a slave system wants to communicate with or through the master system, it must synchronize its frames and frame boundaries with the frames and frame boundaries of the master system. Where multiple slave systems are accessing a master system, each of the systems must synchronize their frames and frame boundaries with those defined by the master system. In that way, each of the various systems will know the defined frames and will also know the slots of an individual frame in which they may transmit or receive their packets of data. Generally, each system will transmit a packet and also receive a packet within each frame.
For enabling the various systems within the TDMA scheme to stay synchronized, each system maintains a frame counter in order to count the frames that are communicated. Essentially, TDMA frames are generally defined strings of digital bits which are recurring at regular intervals. Therefore, each system counts the bits to define the frame, and when a new frame is detected, the system increments the frame counter. Each system cycles a counter using a clock reference to generate the count which establishes the frame count for the system. When the count reaches a level indicating that a frame has been completed, the frame count is incremented and another frame begins.
Because each of these systems are asynchronous, their frames will generally be defined at different times by their specific counters and clock references. Furthermore, their frame counts will vary. When synchronizing the frames between the master system and any slave system, the boundaries to the frames must be reconciled between the two systems. For example the beginning of a frame boundary of the master system may start multiple bits before the beginning frame boundary of a slave system. In order to align the frames, the frame boundaries must be aligned, and therefore the bit difference between the frame boundaries is determined and a bit offset is used in order to align the frames. The bit offset is determined by using a bit count to reflect the offset between the frames of the master and slave systems. Furthermore, the frame counts between the two systems must be aligned.
One particular TDMA communication scheme which is currently gaining popularity is referred to as a BlueTooth scheme. Within a BlueTooth scheme, it is necessary to be able to maintain communications between at least two different unsynchronized units. Each system within the scheme utilizes its own BlueTooth native clock (CLKN) and one or more slave clocks (CLK1, CLK2). Communication connections between various systems within a BlueTooth scheme require each system to be in either a master mode or slave mode. In the master mode, the communication connection utilizes the time determined by the unit's own native clock (CLKN). For communications in a slave mode, individual clocks such as CLK1 and CLK2 are utilized. In the slave mode, the timing for the CLK1 or CLK2 clock is synchronized to the timing data which is received from a master system and specifically is synchronized to the native clock (CLKN) of that master system. Therefore, within such a BlueTooth scheme, each system will generally have to maintain three individual clocks, CLKN, CLK1, and CLK2. Furthermore, counters, such as frame counters are maintained by each system and are associated with each of the various clock signals, CLKN, CLK1, and CLK2. While the BlueTooth scheme has many desirable qualities, it does have various drawbacks associated with the need for the multiple clocks and counters within each system.
Specifically, power consumption is particularly high for operating various different counters and maintaining separate clocks associated with each counter, and with each master/slave communication connection. Furthermore, hardware associated with each system is more complicated due to the necessity of maintaining various different clocks and counters for each associated master/slave communication connection. That is, for each system within the BlueTooth TDMA scheme, three different long term or frame counters have to be maintained and three different bit counters (for frame boundaries) must also be maintained, representing significant power consumption and hardware complexity.
It is therefore one objective of the present invention to simplify the systems utilized within a TDMA scheme, and particularly within a BlueTooth TDMA scheme.
It is another objective of the invention to reduce the power consumed by each system, and also reduce the hardware complexity associated with each system. Since the BlueTooth TDMA scheme will be particularly applicable to portable electronics, it is further desirable to decrease complexity, size, and power consumption parameters associated with systems in the BlueTooth scheme.